Streptococcal adhesion to novel low-shrink silorane-based restorative

ObjectivesThe aim of the present study was to compare the susceptibility of one novel silorane-based and four widely used conventional methacrylate-based resin composites to adhere oral streptococci and to relate any differences to surface roughness, hydrophobicity and type of matrix.MethodsSpecimens of restoratives Filtek Silorane, Filtek Z250, Tetric EvoCeram, Quixfil and Spectrum TPH were prepared (10.0-mm diameter, 2.0-mm height). Surface roughness was assessed by perthometer measurements and hydrophobicity according to water contact angles was determined by computerized image analysis. Bacterial suspensions of Streptococcus oralis, Streptococcus sanguinis, Streptococcus gordonii and Streptococcus mutans were incubated for 2.5 h at 37 °C with 15 test specimens for each material and adhesion was quantified with fluorescence dye Alamar Blue/Resazurin and an automated multi-detection reader. Glass served as reference. Statistical analysis was performed using the Mann–Whitney U-test (α = 0.05).ResultsMedian roughness values of all composites ranged between 0.04 and 0.11 μm, median contact angles between 59.7° and 92.1°. Significantly lowest fluorescence intensities of all test materials were found on Filtek Silorane for three of four streptococcal strains. The fluorescence intensities of the four conventional methacrylate resin composites were significantly higher and comparable among each other.SignificanceWhen compared against four conventional methacrylate composite resins, a general significance to a lower quantity of adhering streptococci was found on the novel silorane-based composite resin, which might result from its increased hydrophobicity. The low adhesion potential of the silorane-based composite may potentially improve the longevity of direct fillings and reduce recurrent caries.     

Mechanical and physical properties of silorane and methacrylate-based composites

ObjectivesThis study measured the degree of conversion (DC), sorption, solubility and microhardness of methacrylate (Filtek Z250 and Filtek Z350XT) and silorane-based composites (Filtek P90).MethodsDC was measured using near infrared spectroscopy immediately and 24 h after the photoactivation. Sorption and solubility measurements were performed after 24 h, 4 weeks and 12 weeks of storage in water. Knoop microhardness was measured after 24 h and after thermal cycling. The data were statistically analyzed using ANOVA followed by Tukey's, Tamhane or paired t-tests (α = 0.05).ResultsThe DC for P90 (37.22 ± 1.46) was significantly lower than the Z250 (71.44 ± 1.66) and Z350 (71.76 ± 2.84). Water sorption was highest in the Z250 and lowest in the P90. All the tested composites exhibited similar values after 24 h of immersion, and no significant differences were observed. No significant differences were observed between the solubilities of the P90 composite (12 weeks) and the Z250 or Z350 composites (4 weeks). KHN values were less elevated for the P90 composite and similar for the Z250 and Z350 composites. An effect of thermal cycling on KHN values was observed for all the composites (p < 0.001).ConclusionsSilorane produced the lowest DC and KHN values and exhibited lower water sorption and solubility compared to methacrylate-based composites. These differences suggest that silorane composites exhibit better hydrolytic stability after 3 months of water immersion compared to conventional methacrylate-based composites.Clinical significanceSilorane had higher hydrolytic stability after 3 months of water immersion than the methacrylate-based resins, despite the lower values of DC and KHN recorded.     

Macro-, micro- and nano-mechanical investigations on silorane and methacrylate-based composites

ObjectivesCationic ring-opening monomers with a reduced shrinkage stress – silorane – are being used as matrix resins for recently introduced dental composites. Since shrinkage and mechanical properties are generally opposite properties, our study aimed to analyze the mechanical behavior of the silorane-based composite in comparison to six homologous clinical successful methacrylate-based composites.MethodsMechanical properties were determined at macro- (strength and modulus of elasticity), micro- (hardness, modulus of elasticity and creep) and nano-scale (nano-dynamic-mechanical parameters: complex, storage, loss modulus and tan δ) after storing the materials for 24 h in distilled water as well as after aging (thermocycling and storing for 4 weeks in water, saliva or alcohol).ResultsThe strongest influence on the mechanical properties at macroscopic scale was exerted by the storage media although the influence of the material was also significant. At micro- and nano-scale, the material itself influenced the mechanical properties stronger than the storage. By comparing the four storage conditions, a multivariate analysis revealed a significant decrease in all measured mechanical properties by storing for 4 weeks in water, saliva or alcohol, when compared to the 24 h storage. The strongest effect was exerted through the alcohol storage, whereas the effect of storing for 4 weeks in water or saliva was comparable. The nano-composites were more degraded by a 4-week storage in water and saliva than the micro-hydrids, whereas the effect of storing in alcohol was material depended.The tested silorane-based composite revealed good mechanical properties. The material was very stable in all applied solvents and more reliable by storing in alcohol solutions than the measured methacrylate-based composites.SignificanceFrom the point of view of the mechanical properties measured at macro-, micro- and nano-scale, the silorane-based composite was comparable to clinically successful methacrylate-based composite materials, encouraging the clinical use of the new composite material.     

Effect of resin matrix composition on the translucency of experimental dental composite resins

ObjectivesThe purpose of this study was to investigate the effect of the resin matrix composition on the translucency of experimental dental composite resins.MethodsThree types of unfilled resin matrices (TEGDMA-, UDMA- and BisGMA-based) were formulated and light cured. In addition, six different experimental dental composite resins with constant filler loading but varying in the type of monomer and the content of BisGMA were fabricated. Discs of each test material with 15.5 mm diameter and 1.0 mm thickness were prepared (N = 3) and light cured. Total and diffuse transmittance values for each sample were measured using a UV/VIS spectrophotometer with the range of readings from 380 to 700 nm. Difference in color was measured using the CIE Lab system.ResultsStatistical analysis by one-way ANOVA followed by Tukey's test showed that there was no statistically significant difference in transmittance values between the three unfilled resins. However, with the addition of filler, BisGMA-containing composite resins showed significantly higher transmittance values than the UDMA- and TEGDMA-based composite resins. Regression analysis revealed that there was a linear correlation between the percentage of BisGMA in the resin matrix and the total and diffuse translucency.SignificanceThe amount of BisGMA used in the resin matrix has a significant effect on the translucency of silica filler-containing dental composite resins.     

Durability of composite repair using different surface treatments

ObjectiveTo evaluate the surface treatment and hydrophilicity of the bonding agent on the composite repair strength (RS), silver nitrate uptake (SNU), surface roughness (SR) and estimation of surface area (SA).MethodsFifty resin blocks (Opallis, FGM) were polished and divided in 5 groups: no treatment (NT); roughening with a fine (FDB); medium (MDB); coarse-grit (CDB) and 50-μm aluminium oxide sandblasting (AO). A hydrophobic (Adhesive, Scotchbond Multi-Purpose Plus, 3M ESPE) or hydrophilic (Adper Single Bond 2, 3M ESPE) adhesive was applied, followed by composite placement (Opallis, FGM). Composite-composite bonded sticks (0.9 mm²) were tested in tension (1.0 mm/min) immediately [IM] or after 6 months [6 M] of water storage. Two sticks from each tooth, at each time, were immersed in a 50% silver nitrate solution and evaluated by SEM. A profilometer was used to measure SR. SEM images were used to estimate the SA using the Image J software. Data were analysed by ANOVA and Tukey's tests.ResultsThe AO showed the highest CR strength for both adhesives, whilst the NT group showed the lowest, irrespective of the storage period. The diamond burs had intermediate performance. Silver nitrate deposits were seen after 6 M for the hydrophilic adhesive. The ranking of SR values (Ra) from the lowest to the highest was: NT < FDB < MDB < AO ≤ CDB. A higher SA was produced by AO treatment.ConclusionsThe AO treatment provides the highest CR strength likely due to the high SA produced. The bonding agent did not seem to affect the CR strength after 6 M, although early signs of degradation were detected for the hydrophilic system.Clinical significancePolished composite should be preferred roughened with aluminium oxide followed by the application of a hydrophobic intermediate agent before composite repair.     

Influence of photoinitiator system and nanofiller size on the optical properties and cure efficiency of model composites

ObjectiveTo establish the relationship between photoinitiator system and nanofiller size on the optical properties and cure efficiency of model composites.MethodsModel composites based on BisGMA/TEGDMA (60:40 mol%) were loaded with 40 wt% of 7 nm or 16 nm-sized filler particles. One of the following photoinitiator systems was added: camphorquinone (CQ) associated with an amine (EDMAB), monoacylphosphine oxide (TPO), or bysacylphosphine oxide (BAPO). The optical properties of disk-shaped specimens were measured 24 h after curing and repeated after storage in water for 90 days and coffee for 15 days. A large spectrum LED unit (Bluephase G2, Ivoclar Vivadent) was used for photoactivation. CIE L*a*b* parameters, color difference (ΔE), and translucency parameter (TP) were calculated. Knoop hardness readings were taken at top and bottom composite surfaces. Cure efficiency was determined by bottom/top hardness ratio. Data were statistically analyzed at α = 0.05 significance level.ResultsComposites formulated with 16 nm particles had higher CIE L* than those with 7 nm particles in all storage conditions. BAPO-based composites generally had lower CIE a* than the other composites. The group TPO + 16 nm before storage and all groups with 16 nm-sized particles after storage had lower CIE b* (i.e. lower degree of yellowing) than the other groups. TPO-based materials had higher color stability. The cure efficiency was not significantly affected by photoinitiator system or particle size. CQ + 7 nm had the lowest and BAPO + 16 nm the highest hardness values.SignificanceCombination of photoinitiator system and filler particle size might affect the optical properties of composites, with low influence on cure efficiency.     

Bond strength durability of a resin composite on a reinforced ceramic using various repair systems

ObjectivesThis study compared the durability of repair bond strength of a resin composite to a reinforced ceramic after three repair systems.MethodsAlumina-reinforced feldspathic ceramic blocks (Vitadur-α^®) (N = 30) were randomly divided into three groups according to the repair method: PR-Porcelain Repair Kit (Bisco) [etching with 9.5% hydrofluoric acid + silanization + adhesive]; CJ-CoJet Repair Kit (3M ESPE) [(chairside silica coating with 30 μm SiO₂ + silanization (ESPE^®-Sil) + adhesive (Visio?-Bond)]; CL-Clearfil Repair Kit [diamond surface roughening, etching with 40% H₃PO₄ + Clearfil Porcelain Bond Activator + Clearfil SE Bond)]. Resin composite was photo-polymerized on each conditioned ceramic block. Non-trimmed beam specimens were produced for the microtensile bond strength (μTBS) tests. In order to study the hydrolytic durability of the repair methods, the beam specimens obtained from each block were randomly assigned to two conditions. Half of the specimens were tested either immediately after beam production (Dry) or after long-term water storage (37 °C, 150 days) followed by thermocyling (12,000 cycles, 5–55 °C) in a universal testing machine (1 mm/min). Failure types were analyzed under an optical microscope and SEM.ResultsμTBS results were significantly affected by the repair method (p = 0.0001) and the aging conditions (p = 0.0001) (two-way ANOVA, Tukey's test). In dry testing conditions, PR method showed significantly higher (p < 0.001) repair bond strength (19.8 ± 3.8 MPa) than those of CJ and CL (12.4 ± 4.7 and 9.9 ± 2.9, respectively). After long-term water storage and thermocycling, CJ revealed significantly higher results (14.5 ± 3.1 MPa) than those of PR (12.1 ± 2.6 MPa) (p < 0.01) and CL (4.2 ± 2.1 MPa) (p < 0.001). In all groups when tested in dry conditions, cohesive failure in the composite accompanied with adhesive failure at the interface (mixed failures), was frequently observed (76%, 80%, 65% for PR, CJ and CL, respectively). After aging conditions, while the specimens treated with PR and CJ presented primarily mixed failure types (52% and 87%, respectively), CL group presented mainly complete adhesive failures at the interface (70%).SignificanceHydrolytic stability of the repair method based on silica coating and silanization was superior to the other repair strategies for the ceramic tested.     

Nanoleakage,ultramorphological characteristics,and microtensile bond strengths of a new low-shrinkage composite to dentin after artificial aging

ObjectivesTo study the microtensile bond strengths and nanoleakage of low-shrinkage composite to dentin. The null hypotheses tested were (1) aging does not affect the bonding of low-shrinkage composite; (2) there is no difference in microtensile bond strengths and nanoleakage using different bonding strategies.Methods32 extracted molars were assigned to one of four groups: LS System Adhesive (LS, 3M ESPE); dentin etched for 15 s with phosphoric acid + LS System Adhesive (LSpa); Adper Single Bond Plus (SB, 3M ESPE); SB + LS Bond (SBLS). Occlusal dentin was exposed and restored with Filtek LS (3M ESPE). The samples were tested after 24 h or after 20,000 thermocycles and 6 months of aging. Teeth were sectioned with a cross-section of 0.8 ± 0.2 mm² and fractured at a crosshead speed of 1 mm/min. The data were submitted to ANOVA/Duncan's post hoc test, at p < 0.05. Five slabs from each group were selected and immersed in 50 wt% ammoniacal silver nitrate. Then, specimens were processed for SEM, the silver penetration was measured and data analyzed with Kruskal–Wallis at p < 0.05.ResultsNo statistically significant difference was found among the experimental groups for the factor dentin treatment (p = 0.165) and aging (p = 0.091). All experimental groups exhibit some degree of nanoleakage. There was no adhesion of Filtek LS applied directly over dentin surfaces treated with SB.SignificanceThe new low-shrinkage resin composite showed compatibility only with its dedicated adhesive. Pre-etching did not improve the bond strengths to low-shrinkage resin composite. Some degree of nanoleakage was evident in all groups.     

Flowability of composites is no guarantee for contraction stress reduction

ObjectivesThe purpose of this study was to measure the contraction stress development of three flowable resin-composite materials (Grandio Flow, VOCO GmbH, Cuxhaven, Germany; Tetric Flow, Ivoclar Vivadent, Schaan, Liechtenstein; Filtek Supreme XT Flowable Restorative, 3 M ESPE, ST. Paul, MN, USA) and an universal micro-hybrid composite resin (Filtek Z250, 3 M ESPE, St. Paul, MN, USA) during photopolymerization with a halogen curing light, using a novel stress-measuring gauge.MethodsCuring shrinkage stress was measured using a stress-analyzer. Composites were polymerized with a halogen curing unit (VIP, Bisco Inc., Schaumburg, IL, USA) for 40 s. The contraction force (N) generated during polymerization was continuously recorded for 180 s after photo-initiation. Contraction stress (MPa) was calculated at 20 s, 40 s, 60 s, 120 s and 180 s. Data were statistically analyzed.ResultsFiltek Supreme XT Flowable Restorative exhibited the highest stress values compared to other materials (p < 0.05), while the lowest values were recorded with Tetric Flow (p < 0.05). Tetric Flow was also the only flowable composite showing stress values lower than the conventional composite Filtek Z250 (p < 0.05).SignificanceFlowable composites investigated with this experimental setup showed shrinkage stress comparable to conventional resin restorative materials, thus supporting the hypothesis that the use of flowable materials do not lead to marked stress reduction and the risk of debonding at the adhesive interface as a result of polymerization contraction is similar for both type of materials.     

Color differences: Polymerized composite and corresponding Vitapan Classical shade tab

ObjectivesThis study compared newer composite resin restorative materials to the Vitapan Classical tabs they purported to represent.MethodsFive Vitapan Classical tabs were studied: A3.5, B2, C1, C3, and D2 (n = 3). These tabs created a variety of levels of lightness, chroma and hue. Each of these five shade tabs was removed from three different shade guides, and an intraoral spectrophotometer was used to capture CIELAB color coordinates. Three separate readings were made and all nine were averaged. The inter-tab color differences were also calculated. Five specimens approximately 4.0 mm thick were fabricated for each of the shades studied using five different composite resin materials. Composite specimens were of the same size and shape as target shade tabs, and three separate recordings were made for each of them. This average was compared to five Vitapan Classical shade tabs to calculate the color differences using both CIELAB and CIEDE2000 color difference formulas. Color differences were compared to thresholds for perceptibility and acceptability reported in other studies.ResultsCIELAB and CIEDE2000 color differences ranged from 3.9 to 22.8 and from 2.1 to 13.8, respectively. None of the materials proved, an acceptable CIELAB color match to any of the shades tested.ConclusionWhen various shade tabs of Vitapan Classical shade guides were compared with correspondent tabs made of direct restorative composites, no material/shade combination resulted in an acceptable mismatch relative to the used standard of acceptability. Therefore, evaluated resin composites exhibited poor match compared to target Vitapan Classical tabs.     

Color change of some aesthetic dental materials: Effect of immersion solutions and finishing of their surfaces

ObjectivesThe purpose of this research was to evaluate the color change of five aesthetic dental materials, before and after immersion in distilled water and blue food color solution for 7 and 21 days, and to study the effect of finishing the surfaces on any color change.MethodsDisc shaped samples of five types of light curing composite (A2) (n = 10 samples/composite) were prepared and all samples were light-cured with a Plasma Arc light cure unit for ten seconds. One side of each sample disc was finished and polished with a Super-Snap system all samples. After 24 h, color measurements of each sample were conducted using a digital spectrophotometer. Five sample discs from each composite group were immersed in 30 ml of food color solution for 7 and 21 days, while the remaining five sample discs were immersed in 30 ml of distilled water as a control. Color measurements were repeated for all samples at 7 and 21 days after immersion. The color changes were statistically analyzed using t-tests within the same group. A result was considered statistically significant at α = 0.05.ResultsThe color differences (ΔE) ranged from 0.4 to 4.66 and statistically significant differences on the finished and unfinished surfaces were observed after immersion in the food color solution for 7 days. No significant differences were found in any group after immersion in the food color solution for 21 days. The Tetric EvoCeram and Arabesk groups showed less color differences after 7 and 21 days than other composites.ConclusionFinished composite surfaces showed less coloration than unfinished surfaces after 7 days, but all surfaces (finished and unfinished) were highly colored for all composite types after 21 days.     

Acoustic emission analysis of the effect of simulated pulpal pressure and cavity type on the tooth–composite interfacial de-bonding

ObjectiveThe aim of this study was to evaluate the influence of in vitro pulpal pressure and cavity type on the tooth–composite bonding interface by means of acoustic emission (AE) analysis.MethodsClasses I and II cavities on extracted third molars were prepared and assigned to four groups of seven teeth each: (1) direct composite restoration without simulated pulpal pressure (SPP) in class I cavity, (2) direct composite restoration with SPP in class I cavity, (3) direct composite restoration without SPP in class II cavity, (4) direct composite restoration with SPP in class II cavity. The teeth were restored with Filtek Z250 composite and Adper Scotchbond Multi-Purpose adhesive system (3M ESPE, St. Paul, MN, USA). AE events were recorded for 2000 s during light-curing. Groups 2 and 4 were subjected to 20 cm H₂O hydrostatic pressure throughout the procedures. The data were analyzed with two-way ANOVA. After the AE test, teeth were sectioned longitudinally in mesio-distal direction, the tooth–composite interface was examined using SEM.ResultsSPP in Groups 2 (4.57 ± 1.40) and 4 (3.43 ± 1.13) yielded significantly higher AE events number than those of Groups 1 (3.43 ± 1.51) and 3 (1.71 ± 0.95) where the SPP was not applied (p < 0.05). The number of AE events of class I cavity in Groups 1 and 2 were significantly higher than those of class II cavity in Groups 3 and 4 (p < 0.05). SEM examination showed that all groups had intact enamel–composite interface, while micro-gaps were observed at the dentin–composite interface, mainly at the pulpal floor of the cavity. The class I cavities with SPP in Group 2 showed wider gaps more frequently than class II cavities without SPP in Group 3.SignificanceThe SPP and class I cavity with high C-factor triggered more AE events, confirming its negative impact on the bonding interface.     

Curing potential and color stability of different resin-based luting materials

PurposeTo determine the curing potential and color stability of resin-based luting materials for aesthetic restorations.Material and MethodsFour resin-based luting agents were tested: traditional dual-activated resin cement (RelyX ARC, ARC), amine-free dual-activated resin cement (RelyX Ultimate, ULT), light-activated resin cement (RelyX Veneer, VEN), and pre-heated restorative resin composite (Filtek Supreme, PHC). Degree of C = C conversion was determined by infrared spectroscopy (n = 3) with direct light exposure or with interposition of 1.5-mm-thick ceramic (e.max Press HT) between the luting material and light. The curing potential considered the ratio between these two scenarios. Color difference (n = 6) was determined by CIELAB (ΔE_ab) and CIEDE2000 (ΔE₀₀) methods, by spectrophotometer measurements made 24 h after photoactivation and 90 days after storage in water. Data was submitted to ANOVA and Tukey’s test (α = 0.05).ResultsThe luting agents affected both conversion and color stability. With ceramic, ARC produced the highest conversion among the tested groups (75 ± 1%) and the pre-heated composite (PHC) the lowest one (51 ± 3%), but the curing potential was similar for all materials. ULT produced lower ΔE_ab than ARC. PHC presented the lowest color difference when considered both CIELAB and CIE2000 methods (ΔE_ab 2.1 ± 0.4; ΔE₀₀ 1.6 ± 0.2).SignificanceAll luting strategies presented high curing potential. Amine-free dual-activated material was able to reduce color difference than that formulated with the amine component. Pre-heated composite produced the least color variation after storage.     

Color and contrast ratio of resin composites for whitened teeth

ObjectivesThe purpose of this study was to determine the optical properties, color and contrast ratio (CR) of commercially available resin composites marketed for the restoration of whitened teeth.MethodsTwenty-six resin composites designed for restoration of whitened teeth and four shade B1 (control) were evaluated. Five resin composite disks (d = 12 mm, h = 1.54 mm) were fabricated for each shade of composite and were stored in water at 37 °C for at least 24 h. A colorimeter was used to measure specimen color over both white and black backgrounds. CIELAB and CIExyY color spaces were used. The CIELAB color notation system provides values for L*a*b*. The CIExyY system provides lightness and chromaticity values, where Y represents lightness and xy chromaticity. The contrast ratio (CR) was assessed using, CIE xyY, of the specimens against black (Yb) and white (Yw) backgrounds, with CR = Yb/Yw. The data for L*, a*, b* and CR were analyzed by one-way ANOVA, Tukey's test, and the correlation L* and CR was analyzed by Pearson correlation test (α = 0.05).ResultsSignificantly different L*, a*, b* values and CR were observed. Premise XL2 had the highest L* and CR values and Vit-l-escence PS had the lowest. Vit-l-escence PS had the highest a* value and Point 4XL2 had the lowest, Premise XL1 had the highest b* value and Supreme WB the lowest. The L* and CR correlation was positive and statistically significant.ConclusionsComposites designated for whitened teeth have different levels of color and contrast ratio. Awareness of the optical properties of the composites allows the operator to choose the appropriate materials to mimic the remaining tooth structure.     

Effect of proanthocyanidin incorporation into dental adhesive resin on resin-dentine bond strength

ObjectivesThis study evaluated the effect of proanthocyanidin (PA) incorporation into experimental dental adhesives on resin–dentine bond strength.MethodsFour experimental hydrophilic adhesives containing different PA concentrations were prepared by combining 50 wt% resin comonomer mixtures with 50 wt% ethanol. Proanthocyanidin was added to the ethanol-solvated resin to yield three adhesives with PA concentrations of 1.0, 2.0 and 3.0 wt%, respectively. A PA-free adhesive served as the control. Flat dentine surfaces from 40 extracted third molars were etched with 32% phosphoric acid. The specimens were randomly assigned to one of the four adhesive groups. Two layers of one of the four experimental adhesives were applied to the etched dentine and light-cured for 20 s. Composite build-ups were performed using Filtek Z250 (3M ESPE). After storage in distilled water at 37 °C for 24 h, twenty-four bonded teeth were sectioned into 0.9 mm × 0.9 mm beams and stressed to failure under tension for bond strength testing. Bond strength data were evaluated by one-way ANOVA and Tukey's test (α = 0.05). Interfacial nanoleakage was examined in the remaining teeth using a field-emission scanning electron microscope and analysed using the Chi-square test (α = 0.05).ResultsNo significant difference in bond strength was found amongst PA-free, 1% and 2% PA adhesives. However, incorporation of 3% PA into the adhesive significantly lowered bond strength as demonstrated by a greater number of adhesive failures and more extensive nanoleakage along the bonded interface.ConclusionIncorporation of 2% proanthocyanidin into dental adhesives has no adverse effect on dentine bond strength.Clinical significanceThe addition of proanthocyanidin to an experimental adhesive has no adverse effect on the immediate resin–dentine bond strength when the concentration of proanthocyanidin in the adhesive is less than or equal to 2%.     

Fracture strength and fatigue resistance of dental resin-based composites

ObjectivesThe aim of this study was to evaluate in vitro the influence of fiber-reinforcement on the fracture strength and fatigue resistance of resin-based composites.MethodsOne hundred rectangular bar-shaped specimens (2 mm × 2 mm × 25 mm) made of resin-based composite were prepared in a stainless steel split-mould: (i) thirty specimens of particulate filler composite (PFC) (Filtek Z100, 3 M ESPE, St Paul, MN, USA), (ii) thirty specimens of fiber-reinforced composite (FRC) (Everstick C&B, Sticktech Ltd., Turku, Finland) and (iii) forty specimens of PFC and FRC combined in two longitudinal layers of equal thickness. Each specimen was trimmed into a cylindrical hourglass shape. The fracture strength (cantilever beam test, n = 10) and the fatigue resistance (rotating cantilever beam test; staircase method: 10⁴ cycles, 1.2 Hz, n = 20) were determined. Fracture strength, fatigue resistance and work-of-fracture were calculated. The fracture surfaces of failed specimens were analyzed with SEM. Data was analyzed by logistic regression, one-way ANOVA followed by Tukey's post hoc test and, a Student's t-test.ResultsANOVA revealed that fiber-reinforcement had significant effect (P < 0.001) on fracture strength, fatigue resistance, and work-of-fracture. Student's t-test showed significant differences (P < 0.001) in fatigue resistance compared to fracture strength.ConclusionsWithin the limitations of this study, the following conclusions can be drawn (i) the fatigue resistance of resin-based composites is lower than their fracture strength and (ii) FRC are more fatigue resistant than PFC or combinations of FRC and PFC.     

R-curve behavior and toughening mechanisms of resin-based dental composites: Effects of hydration and post-cure heat treatment

ObjectivesTo test the hypothesis that the fracture resistance of two different particulate resin composites degrade after water hydration and improve after post-cure heat treatment, and to correlate those changes with salient failure micromechanisms.MethodsTwo composites with different filler morphology were selected, denoted microhybrid (Filtek? Z250) and nanofill (Filtek? Supreme plus). Following initial light curing, hydrated samples were aged in water for 60 days at room temperature while post-cured samples were heat treated at 120 °C for 90 min. Fracture resistance was assessed using fracture resistance curves (R-curves) utilizing pre-cracked compact tension, C(T), specimens. The flexural strength of the hydrated composites also was evaluated in four-point bending using unnotched beams. Scanning electron microscopy (SEM) of crack paths and fracture surfaces was performed to determine the micromechanisms of fracture and toughening. The results were compared by two-way ANOVA and Tukey's multiple comparison test (p ≤ 0.05).ResultsSEM observations revealed a predominantly interparticle matrix crack path for all cases except the hydrated nanofill composite, which showed evidence of particle matrix debonding. Hydration lowered the strength for both composites and the peak toughness for the nanofill composite. The strength decrease was attributed to resin matrix plasticization and hydrolytic degradation in both cases, with additional interfacial degradation causing a larger strength decline and concomitant peak toughness decrease in the nanofill composite. The post-cure heat treatment noticeably changed the R-curve shape causing the peak toughness to be reached after shorter amounts of crack extension. Such changes help explain the increases in strength reported in other studies and is attributed to improved resin matrix properties.SignificanceResults from this study provide new insight into the micromechanisms of fracture in resin-based dental composites which should aid the future development and improvement of these materials.     

Fatigue limits of enamel bonds with moist and dry techniques

ObjectiveShear fatigue limit (SFL) testing, coupled with shear bond strength (SBS) measurements can provide valuable information regarding the ability of adhesive systems to bond to mineralized tooth structures. The clinical technique for enamel bonding with adhesive resins has shifted from bonding to a thoroughly dried acid conditioned surface to a moist surface to facilitate dentin bonding. The purpose of this study was to compare the performance of ethanol-containing etch-and-rinse adhesive (ERA) systems on moist and dry enamel by determining the resin composite to enamel SBS and SFL, and examining the relationship of SBS and SFL.MethodsTwelve specimens each were used to determine 24-h resin composite (Z100 – 3M ESPE) to enamel SBS to moist and dry surfaces with two ERA systems, Adper Single Bond Plus (SBP) and OptiBond Solo Plus (OBP). A staircase method of fatigue testing was used in a four-station fatigue cycler to determine the SFL of resin composite to enamel bonds (moist and dry) with the two ERA systems (20 specimens for each test condition) at 0.25 Hz for 40,000 cycles. ANOVA and Tukey's post hoc test were used for the SBS data and a modified t-test with Bonferroni correction was used for comparisons of SFL.ResultsThe two ERA systems each generated statistically similar SBS (p > 0.05) to moist and dry enamel and the SBS of SBP was significantly higher than OBP on dry enamel (p < 0.05). The SFL of SBP was significantly greater to dry enamel when compared to moist enamel and there was not a significant difference in the SFL of OBP on dry and moist enamel. There were no significant differences in SFL values between SBP on either moist or dry enamel and OBP on both moist and dry enamel.SignificanceFatigue testing may provide more useful information than SBS tests regarding the performance of dental adhesive systems. The chemical composition, solvents and filler components of ERA systems may influence their ability to develop long-term durable bonds to both moist and dry enamel surfaces.     

Comparison of four silane primers and an isocyanate primer for bonding of tri-n-butylborane resin to a leucite-reinforced glass ceramic

PurposeThe purpose of the present study was to compare the effectiveness of an isocyanate monomer and four different silane monomers as primer components for bonding a leucite-reinforced glass ceramic (GN-Ceram Block).MethodsFour different methyl-methacrylate based primers, each with three different concentrations (1, 4, or 16wt%) of 2-methacryloxyethylisocyanate (MOI), 3-methacryloxypropylmethyldimethoxysilane (MDS), 3-methacryloxypropyltrimethoxysilane (MTS), and 3-acryloxypropyltrimethoxysilane (ATS) were prepared. A commercially available silane primer (ESPE?Sil) was also used as a control. The GN-Ceram Block specimen was ground with silicon carbide paper, rinsed, primed, and then bonded to a resin composite disk using a tri-n-butylborane-initiated self-curing luting agent. After 24-h immersion in water, the shear bond strengths were determined.ResultsThe highest level of bond strength was obtained with 4wt% MTS (45.2 MPa) and 4wt% ATS (38.7 MPa), followed by 4wt% MOI (29.8 MPa), ESPE?Sil (28.1 MPa), and 4wt% MDS (27.9 MPa). For each MTS, ATS, MOI, and MDS, the bond strengths for concentrations of 4wt% and 16wt% were not significantly different. No significant differences were found between 4wt% ATS, 4wt% MOI, ESPE?Sil, and 4wt% MDS. The use of any of these primers led to a significant increase in bond strength compared to an unprimed control (13.8 MPa).ConclusionsThe type and concentration of monomers dissolved in the primer influence the bond strength between a tri-n-butylborane resin and a leucite-reinforced glass ceramic GN-Ceram Block. The effectiveness of MOI was found to be comparable to that of MDS, ATS, and ESPE?Sil, but inferior to that of MTS.     

Effect of composition, viscosity and thickness of the opaquer on the adhesion of resin composite to titanium

ObjectivesThe objectives of this study were to determine the bond strength of powder-liquid and paste opaquers with different chemical compositions and viscosity to a metal substructure when they were applied in two thicknesses and to evaluate the failure modes after the bond strength test.MethodsTitanium plates (51 mm × 25 mm × 1 mm) (n_plates = 25, N = 80, n = 10 per group) were conditioned with chairside silica coating (CoJet-Sand, 30 μm silica coated Al₂O₃) from a distance of approximately 10 mm at a pressure of 2.8 bar for 15 s/cm² and silanized. Four types of opaquers, namely one powder-liquid (Sinfony, 3 M ESPE), and three paste opaquers [(Cimara, Voco), (Monopaque, Ivoclar Vivadent), (Cavex Experimental, Cavex)] were applied either in 0.25 or 0.50 mm thicknesses using standard polyethylene molds and photo-polymerized. Resin composite (Quadrant Posterior Dense, Cavex) was applied incrementally and photo-polymerized. The specimens were thermocycled (5–55 °C, 6000 cycles) prior to shear bond strength test (1 mm/min). Failure types were analyzed using an optical microscope and scores were given according to the modified Adhesive Remnant Index (ARI) (Score 0 = no opaquer on the surface, Score 1 = <1/2 covered with opaquer, Score 2 = >1/2 covered with opaquer, Score 3 = completely covered with opaquer).ResultsWhile thickness did not significantly affect the bond strength results (p = 0.523), type of opaquers had a significant influence on the results (p < 0.01) (Univariate ANOVA, Tukey's test). Interaction terms between thickness and opaquer type were significant (p < 0.01). Debonded specimens during thermocycling were considered as 0 MPa. At both 0.25 and 0.5 mm thicknesses, powder-liquid based opaquer (Sinfony) showed significantly higher results (8.4 ± 5.6 and 8.4 ± 4.9 MPa, respectively) than those of other opaquers (1.4 ± 1 to 4.3 ± 3.8 MPa) (p < 0.05). Only when Cimara was applied in 0.25 mm (6.9 ± 4.2 MPa), there were no significant differences with Sinfony (p > 0.05). The lowest results in both thicknesses were obtained from Monopaque (4 ± 3.8 to 1.6 ± 1 MPa, respectively) and Cavex (1.4 ± 1 to 4.2 ± 2.9 MPa, respectively) paste opaquers. In all opaquers, the incidence of Score 0 (30) was more frequent followed by Score 1 (27) and Score 2 (20).SignificanceThe use of powder-liquid opaquer in order to mask the metal in repair actions provided higher bond strength than those of the paste opaquers in both thin and thick applications. In all opaquers, the incidence of adhesive failure between the opaquer and the metal was more common implying inadequate adhesion.